HA & IPv6

I've just had a thought... IPv6 addresses are generated by the host
machine, from combining the router & the interface's MAC address.
Yes, IPv6 supports on-the-fly address changes, but from what I
understand, that's through a transition mechanism, which might not
be suitable for HA, if you wanted to fail-over a network connection.
(Unless the router had some kind of forwarding mechanism.)
Current HA software probably doesn't handle IPv6 at all, yet, but
presumably it will, eventually. What -would- the impact on HA be
from IPv6? Would it make it slower/more complex/less robust?
Jonathan Day